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Consultants update county on Big Valley hydrologic model to protect Clear Lake hitch spawning
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Summary
O'Connor Environmental and county partners updated the Board on a surface water–groundwater hydrologic model for Big Valley to evaluate streamflow and habitat for the Clear Lake hitch; the model will be calibrated this summer and used to test scenarios affecting spawning flows.
Consultants with O'Connor Environmental and county staff briefed the Lake County Board on April 7 about a multi-year integrated hydrologic modeling study covering Big Valley watersheds and groundwater that is intended to inform strategies for maintaining streamflows during the Clear Lake hitch spawning season.
Presenters said the model integrates streamflow gauge data, groundwater elevations, LiDAR-derived channel geometry, well completion reports and agricultural water-use datasets to relate surface and subsurface processes. The model domain covers the Big Valley groundwater basin with high spatial resolution (approximately 1.6-acre grid cells) and will simulate daily conditions for a 2015–2025 period to capture dry and wet years. The work includes coordination with tribal partners and the California Department of Fish and Wildlife to identify stream reaches important for hitch spawning.
Consultants said monitoring and data-collection work is largely complete; the technical modeling and calibration phases are underway and scenario analyses will start later this summer and fall. Scenario analysis will ask how different water uses and management strategies — including reductions in groundwater pumping or changes in diversions — affect streamflow and habitat connectivity for hitch during key spawning months.
Big Valley tribal partners and the Big Valley Band of Pomo Indians (Sarah Ryan, speaker 31) told the board the tribe has contributed years of monitoring data, including pressure-transducer groundwater and flow monitoring, and has performed thousands of fish rescues during low-flow conditions. The tribe indicated it will share flow and groundwater datasets to help calibrate and validate the model.
Supervisors asked about including climate-change projections in future work; consultants said the initial implementation focuses on the 2015–2025 observational record but noted the modeling framework can be extended to climate scenarios in later phases. The board recorded no action on the presentation; staff said a public follow-up is planned when scenario results are available.
